In present-day communication networks, in particular in communication networks configured as a telephone network, it is known not only for private branch exchanges to be connected to public switching devices but also for a number of subscriber lines to be combined to form a “Multi Line Hunting Group”—also referred to hereafter as “MLHG”—replicating the function of a private branch exchange. An MLHG is assigned a group call number or pilot call number—also referred to as “Pilot Directory Number” or “Pilot DN”—shared by all the grouped-together subscriber lines, after the selection of which—for example for setting up a communication relationship with one of the communication terminals assigned to the MLHG—within the group a free subscriber line is found with the aid of a defined search procedure—referred to hereafter as a “Hunting Algorithm”—for setting up the connection.
In the case of an MLHG, the same search procedures or hunting algorithms as in the case of classical private branch exchanges can be used, for example                “Sequential Hunting” (selection of the first free subscriber line, always beginning from a defined starting point),        “Circular Hunting/Uniform Call Distribution (continuing the search after the last-found, free subscriber line),        “Non-sequential Hunting” (selection of the subscriber line which has been free for the longest),        “Stochastical Hunting” (selection of a free subscriber line on the random principle).        
The MLHG is of interest in particular for small and medium-sized companies which require call distribution in connection with a pilot call number in the manner of a private branch exchange, but do not wish to invest in private switching devices or branch exchanges.
However, an MLHG has the disadvantage that the subscriber lines combined to form an MLHG have to be physically assigned to the same switching device, which means a local restriction of the MLHG or of the group-specific service features provided by the MLHG.
Within the framework of the ITU Specification ITU-T Q.82.4, an extension of the provision of group-specific service features is mentioned, for example extension of search algorithms or hunting algorithms to a number of switching devices or network nodes—, but so far no solution has been disclosed.
Within present-day telephone networks, the signaling for the setting-up and clearing-down of 64-kbit user channel connections for controlling ISDN services takes place on the basis of the ITU-T signaling system No. 7—also referred to as SS NO.7.
The actual task of the signaling protocol No. 7 is the exchange of signaling messages within the communication networks. The signaling messages are exchanged by the user parts within the reference model. Depending on the type of signaling messages, a distinction is made, for example, between the Telephone User Part—TUP the Data User Part—DUP—, the ISDN User Part—ISUP—and the Broadband ISDN User Part—B-ISUP. The TUP was implemented as the first application in the signaling protocol No. 7. Building on the basis of the TUP for generally establishing the ISDN and for establishing the signaling within the ISDN, the ISUP was defined.
The ISUP gave rise, as the latest application, to the B-ISUP for applications within ATM-based networks. The main tasks of the ISUP are:                setting up and clearing down user channel connections,        handling the signaling for supplementary services,        coupling two “logical” signaling connections (for example on transfer from the national network into the international network).        
The ISDN user part makes use directly of the message transfer part—MTP—and of the control part for signaling connections—SCCP, layer 4—, the ISUP itself is consequently to be classified as belonging to layers 4 to 7 in the OSI reference model. The ISDN user part controls both the link-by-link signaling for reaching the destination and the end-to-end signaling relationship between the originating switching point and the destination switching point. With the aid of the link-by-link signaling, the path for the user channel connection and the signaling connection is sought and, after corresponding commands, is set up. The MTP is used for this purpose. For the user channel connection, all the involved switching points must be informed, for example about the switching through of the user channel, while only the originating switching point and the destination switching point exchange signaling information for the control of the supplementary services. For the end-to-end signaling, the ISUP makes use of the services of the SCCP. In the ISDN user part, the actual signaling information is exchanged. All the lower-lying layers ensure that this information is transferred in an acknowledged form and reaches the addressed user part. For the exchange of the end-to-end signaling messages for handling ISDN supplementary services, the end-to-end signaling of the SCCP is used on the basis of a TCAP dialog.
For more complex applications within communication networks, such as for example for supporting data bank inquiries in the case of services of the Intelligent Network—also referred to as IN—or in the case of mobile radio applications, the Transaction Capabilities Application Part—TCAP—was introduced into signaling procedure No. 7. For example, the freephone service of the Intelligent Network is used by the initiator of the connection to dial an IN call number (0130 or 0800), which determines a destination call number by a call to the Intelligent Network in dependence on the customer parameters. For the determination of the valid destination call number, only signaling messages have to be exchanged; the user channel is not switched to the IN. This service call is, for example, a typical TCAP application. In the communication of TCAP entities, a distinction is made between structured dialog and unstructured dialog. In the case of structured transport, a transaction relationship is commenced before the exchange of messages and the transaction identification—also referred to as transaction ID—is issued in both communication devices of the two signaling nodes involved for the identification of this relationship. After a BEGIN message, individual items of information are transferred in the structured dialog by CONTINUE messages. The BEGIN message contains the transaction identification of the initiator, the CONTINUE messages contain, according to the direction of transfer, the identification of the initiator or that of the communication partner as the originating identification and the identification of the communication partner as the destination identification. After the transfer of information, the dialog is routinely ended by the END message. The structured dialog is used, for example, for data bank inquiries, such as for example in mobile radio networks or in the IN; all the exchanged messages can be marked by the transaction identification as belonging to this activity.
An intelligent network or IN is a concept comparable to an architecture for introducing complex services into existing telecommunication networks, the architecture describing the structure of an actual IN implementation. The architecture is designed in such a way that it is suitable as a uniform basis for a large number of different services. Supplementing the conventional telecommunication networks, the architecture of intelligent networks represents a platform on which the actual services are based. In the standardization, three (physical) levels were established, to which the various components and functions of the conceptual model of an Intelligent Network are assigned.
The platform implemented by the architecture of the IN comprises not only hardware components, but also a software platform, on which very specific services can be developed by the IN operators by means of suitable aids and can be loaded into the hardware components. The hardware of intelligent networks primarily comprises switching points of the telephone network—also referred to as SSP or Service Switching Points, which detect the actual call of an IN service and direct it to a corresponding SCP—also referred to as a Service Control Point. The actual service runs on an SCP, a very powerful computer with a large, complex data bank, by which many inquiries can be handled in a short time. For the operation of the services, a further level is required, which is also referred to as the SMP or Service Management Point. The SMPs can be used by service customers to dial into the Intelligent Network and change or adapt their respective setting data or parameters for the respective service.
A service switching point implementing service switching functions detects IN calls and forwards the inquiries to the corresponding SCP. The SCP is a digital switching point with special control programs (for example all telecommunication points of a specific level). The call of an IN function is coupled in the control of the switching point by means of predefined triggers. In this case, not only certain call numbers can represent a so-called trigger point—also referred to as a trigger detection point—, it is also possible for certain states of the connection—for example encountering a busy subscriber, subscriber does not answer and so on—to be coupled with IN trigger points. In the simplest case, just the lifting of a telephone without further dialing is enough to initiate an IN trigger. Further actions—for example dialing the call number—can already be assessed by IN. The communication of a number of SSPs with an SCP takes place by means of No. 7 messages, for example by means of TCAP or INAP dialog.
In an SCP or Service Control Point, functions for detecting and controlling IN services are implemented. An SCP is formed by one or more computer systems, by which the IN services are detected and correspondingly controlled. An SCP forwards for example the traffic routing information to the corresponding SSP and determines the charges incurred for the use of the corresponding ISDN services.
The IN services of the SCP are set up, changed, managed and monitored by the Service Management Point or SSP implementing the service management functions, it being possible for all the parameters—for example call numbers, time dependence etc.—to be set and changed by means of the SMP.
The IN elements described—SSP, SCP, SMP—essentially influence the control of connections within a communication network. With the aid of the signaling protocol No. 7, the signaling of the connections to the SCP to be switched within the communication network is diverted, but not the user channels.
The user channels are switched within the telecommunication network on the basis of the control functions implemented by the IN. For certain services, however, inclusion of the user channels is also required. For example, if subscriber inquiries have to be carried out, certain announcements controlled by the IN system have to be activated and, if appropriate, responses to a predetermined possible selection or an identification of the subscriber have to be recorded. The responses of the user are often given in the form of DTMF signals, which are likewise sent in the user channel. For these special tasks, special devices are provided within the IN architecture, having the user channels on one side and signaling connections to the IN on the other side. Such special devices are referred to as Intelligent Peripherals or IPs. These do not have to be restricted to the playing of predetermined announcements or the recording of DTMF signals. In future, systems of this type can also be extended to voice recognition systems or data-oriented systems. The bringing together of different IN functions, in particular the functions of SCP and SSP, is also referred to as a Service Node or SN.